Value-added
utilization practices for composted manures
Dr. Harry Hoitink
The Ohio State University
Composted sewage sludge is used widely by the nursery industry in potting mixes and ground beds to improve soil moisture retention, plant growth and suppress plant diseases. Composted sludges must pass pathogen and heavy metals standards before they can be released to the public. The same federal rules do not apply to sewage sludges applied to land that have not been composted before their application although other regulations govern these byproducts. Negative publicity on sludges in the press typically does not describe these differences in risks associated with composted versus non-composted sewage sludges. As a result, the safety aspects associated with utilization of all types sewage sludges is being questioned today even though it has been shown many times that composted sludges provide beneficial rather than negative environmental effects.
Some nurseries are now actively pursuing alternatives to composted sewage sludges. Composted livestock manures have the potential to replace composted sludges. However, a consistent, high quality product is required in this value-added market. Research performed with funding from the Ohio Water Development Authority at the OARDC/OSU is now developing quality standards for composted dairy and swine manures for these markets. Impacts of changes in parameters such as volatile solids, pH, total nitrogen, carbon to nitrogen ratio, and ammonia emissions during the composting process on plant growth are being evaluated for different manure and bulking agent combinations. The objective is to provide quality control guidelines that will allow composters to accurately evaluate compost maturity and its application rate so that products can be produced that consistently meets the needs of the industry. Results indicate that the quality of composts prepared from cow manure amended with straw as bedding is more predictable than that of manure mixed with sawdust. Furthermore, either type of compost can suppress common root rots as well as induce systemic resistance to foliar diseases in plants. Thus, diseases in the foliage as well as those of plant roots can be minimized.